AdvenOfCode2022/src/prob5.rs

use std::collections::VecDeque;

use itertools::Itertools;
use nom::{
    branch::alt,
    bytes::complete::{tag, take, take_while1},
    combinator::{all_consuming, map, map_res, opt},
    Finish,
    IResult, sequence::{delimited, preceded, tuple},
};

#[derive(Debug)]
struct Instruction {
    quantity: usize,
    src: usize,
    dst: usize,
}

/// Used to parse a crate
///
/// # Arguments
///
/// * `i`:
///
/// returns: Result<(&str, char), Err<Error<I>>>
///
fn parse_crate(i: &str) -> IResult<&str, char> {
    let first_char = |s: &str| s.chars().next().unwrap();
    let f = delimited(tag("["), take(1_usize), tag("]"));
    map(f, first_char)(i)
}

fn parse_hole(i: &str) -> IResult<&str, ()> {
    // `drop` takes a value and returns nothing, which is
    // perfect for our case
    map(tag("   "), drop)(i)
}

fn parse_crate_or_hole(i: &str) -> IResult<&str, Option<char>> {
    alt((map(parse_crate, Some), map(parse_hole, |_| None)))(i)
}

fn parse_crate_line(i: &str) -> IResult<&str, Vec<Option<char>>> {
    let (mut i, c) = parse_crate_or_hole(i)?;
    let mut v = vec![c];

    loop {
        let (next_i, maybe_c) = opt(preceded(tag(" "), parse_crate_or_hole))(i)?;
        match maybe_c {
            Some(c) => v.push(c),
            None => break,
        }
        i = next_i;
    }

    Ok((i, v))
}

fn transpose_rev<T>(v: Vec<Vec<Option<T>>>) -> Vec<VecDeque<T>> {
    assert!(!v.is_empty());
    let len = v
        .iter()
        .max_by(|x, y| x.len().cmp(&y.len()))
        .unwrap_or_else(|| panic!(""))
        .len();

    let mut iters: Vec<_> = v.into_iter().map(|n| n.into_iter()).collect();
    (0..len)
        .map(|_| {
            iters
                .iter_mut()
                .filter_map(|n| n.next())
                .flatten()
                .collect::<VecDeque<T>>()
        })
        .collect()
}

fn parse_number(i: &str) -> IResult<&str, usize> {
    map_res(take_while1(|c: char| c.is_ascii_digit()), |s: &str| {
        s.parse::<usize>()
    })(i)
}

fn parse_pile_number(i: &str) -> IResult<&str, usize> {
    map(parse_number, |i| i - 1)(i)
}

fn parse_instruction(i: &str) -> IResult<&str, Instruction> {
    map(
        tuple((
            preceded(tag("move "), parse_number),
            preceded(tag(" from "), parse_pile_number),
            preceded(tag(" to "), parse_pile_number),
        )),
        |(quantity, src, dst)| Instruction { quantity, src, dst },
    )(i)
}

fn parser(content: &str) -> (Vec<VecDeque<char>>, Vec<Instruction>) {
    let mut lines = content.lines();
    let crate_lines = (&mut lines)
        .map_while(|line| {
            all_consuming(parse_crate_line)(line)
                .finish()
                .ok()
                .map(|(_, line)| line)
        })
        .collect();

    let crate_columns = {
        let mut tmp = transpose_rev(crate_lines);
        tmp.iter_mut().for_each(|item| {
            item.make_contiguous();
        });
        tmp
    };

    assert!(lines.next().unwrap().is_empty());

    let instructions = lines
        .map(|line| all_consuming(parse_instruction)(line).finish().unwrap().1)
        .collect::<Vec<Instruction>>();
    (crate_columns, instructions)
}

pub fn solve_part1(file_path: &str) -> String {
    let content = std::fs::read_to_string(file_path).unwrap_or_else(|err| panic!("{err}"));
    let (mut crate_columns, instructions) = parser(&content);
    instructions.iter().for_each(|ins| {
        (0..ins.quantity).for_each(|_| {
            let tmp = crate_columns
                .get_mut(ins.src)
                .unwrap_or_else(|| panic!("Index {} is out of bound of crate_columns.", ins.src))
                .pop_front()
                .unwrap_or_else(|| panic!("Could not pop front the column {}", ins.src));
            crate_columns
                .get_mut(ins.dst)
                .unwrap_or_else(|| panic!("Index {} is out of bound", ins.dst))
                .push_front(tmp);
        });
    });

    crate_columns
        .iter()
        .map(|item| item.front().unwrap())
        .join("")
}

pub fn solve_part2(file_path: &str) -> String {
    let content = std::fs::read_to_string(file_path).unwrap_or_else(|err| panic!("{err}"));
    let (mut crate_columns, instructions) = parser(&content);
    instructions.iter().for_each(|ins| {
        let mut test = vec!['\0'; ins.quantity];
        (0..ins.quantity).for_each(|i| {
            test[i] = crate_columns[ins.src]
                .pop_front()
                .unwrap_or_else(|| panic!("Could not pop front the column {}", ins.src));
            //crate_columns[ins.dst].push_front(tmp);
        });
        test.reverse();
        test.iter_mut()
            .for_each(|tmp| crate_columns[ins.dst].push_front(*tmp));
    });
    crate_columns
        .iter()
        .map(|item| item.front().unwrap())
        .join("")
}